1. Technical Field
The present invention relates to a unit circuit suitable for driving a driven element, such as an organic light-emitting element and a liquid crystal element, or an electronic element, to a method of controlling the unit circuit, to an electronic device such as an electro-optical device, and to an electronic apparatus.
2. Related Art
Transistors have been generally used to actively drive electro-optical elements, such as liquid crystal elements, organic electroluminescent elements (organic light emitting diode; hereinafter, referred to as ‘OLED element’), or the like. However, the transistors need to be precisely controlled to realize high performance and multiple gray-scale levels.
Low-temperature polysilicon (LTPS) transistors have been used as such driving transistors in the related art; however, in recent years, amorphous silicon transistors have been drawing attention as the driving transistors in that a manufacturing cost can be reduced and uniform characteristics can be easily obtained. However, in the amorphous silicon transistors, when either positive voltages or negative voltages are continuously applied to the gate electrode, the threshold voltage thereof varies, which, for example, changes the brightness of the OLED elements, deteriorating the display quality.
This is because the characteristics of the transistors vary due to, for example, carriers stored as the carriers are continuously supplied to the transistors. Such a phenomenon is particularly noticeable in a case in which the amorphous silicon transistors are used as driving transistors. A technique for applying a negative voltage to a gate electrode of the driving transistors after applying a positive voltage thereto in order to stabilize the characteristics thereof is disclosed in Bong-Hyun You et al., “Polarity-Balanced Driving to Reduce Vth Shift in a Signal for Active-Matrix OLEDs”, SID Symposium Digest of Technical Papers, USA, Society for Information Display, vol. 35, No. 1, pp. 272-275, May, 2004 (refer to FIGS. 3A and 3B).
However, in the technique, two driving transistors and two capacitive elements corresponding to the two driving transistors are needed, so that the circuit configuration becomes complicated. In particular, as the number of circuit elements, such as transistors or capacitive elements, increases, the circuit area becomes larger in proportion to the increased number, which reduces the aperture ratio.
Further, in the technique, since the negative voltage is supplied to the gate electrode of the driving transistor separately from the positive voltage, the circuit configuration is complicated. In addition, the dynamic range of the voltage becomes wide, so that the load on the circuit or the power consumption increases.